This invention relates to a code symbol for marking plastic bottles.
From DE-PS 36 26 775 it is basically known for multiple trip containers to be provided with a supplementary coding during each return. No solution is shown here for the problem of arranging the coding so that it can be detected in as error-free and also space-saving a manner as possible. The latter is especially important, because the quantity of data which has to be introduced onto the container during the life of the container, as data concerning the container itself and the filling, is on the increase, and because moreover, ever smaller containers (e.g. 0.3 liter PET bottles) have to be able to be marked in this way.
From EP-A 354 362 it is known for PET bottles to be provided with code symbols by means of a laser, and a special code-reading process is known from DE-OS 29 43 811.
DE-OS 30 32 520 describes an arrangement for the control of the length of use of cylindrical containers, more especially kegs. Kegs for the drinks industry require recalibration at predetermined time intervals, e.g. after eight years in each case. The known arrangement makes it possible to control the time of putting cylindrical containers in operation with regard to the necessity for recalibration of the container. To this end, each container carries in a first imaginary circle a position marking, with which a first scanning head is coordinated. In a second imaginary circle, the container carries code symbols in the form of lines which state the commissioning time, and with which a second scanning head is coordinated. The container is made to rotate about its axis of symmetry, and the first scanning head switches on the second scanning head when the position marking is detected, in its turn the second head switching on a marking reader. The code symbols for the commissioning time are composed of a number of lines, on account of which the scanning head detecting them operates with a counter, and the number of lines detected represents a measure of the commissioning time of the container. Each recalibration is retained by introducing a new code symbol. Comparison of the counter result with a control value then produces a measure of whether the container being inspected has been in operation already for a length of time which makes a recalibration necessary. If the necessity for recalibration is determined, the relevant container is separated and conveyed for calibration in another device, in which the new code symbol is also introduced. This introduction of the new code symbol takes place in a manner and at a location which are not described in DE-OS 30 32 520. Moreover, the introduction of a new code symbol takes place at any interval in relation to the preceding code symbols, which is adequate in the case of the known arrangement, as the code symbols are merely counted. The code in the known marking process, which is composed of the code symbols, obviously does not have a data content extending beyond the number of recalibrations which have taken place or the years which have passed since the commissioning of the container.
From DE-OS 36 23 475 is known a process for the recognition of mainly rotationally symmetrical objects, more especially containers, which are provided with code symbols, which process serves to recognise transport containers, e.g. in the drinks industry, which are provided with an individualizing marking, from which, amongst other things, the owner and the commissioning time can be seen, in order to be able to follow the path of empties. This known process relates less, however, to code assembly, but more to the removal of the problem of being able to read the coding reliably when it has no accurately predetermined position in relation to an optical sensor. In order to remove this problem, the code symbols in the known process are arranged as radially running bars with a luminance factor differing from the surroundings, the bars being disposed circularly around a centre point. The bars are scanned, and from the scanning signals a mean value is obtained. The signals are binarized using a threshold value derived from the mean value, and the binary signals are decoded. The circular ring of the code symbols is here divided into identical sectors provided in each case for one code symbol, and a certain number of sectors is provided for representing one point of a data word in each case. In this known process, it is neither intended nor possible to mark containers with new code symbols, with the aid of which it might later be ascertained whether a container has to be refilled or discarded.
In the drinks industry, refillable plastic bottles, more especially PET bottles, in which the number of refillings is limited, are being introduced more and more instead of glass bottles. Such refillable plastic bottles must therefore be discarded if the number of round trips has reached the limiting value. This, on the other hand, necessitates the plastic bottles being provided with at least one new code symbol before each round trip, and therefore with each filling, so that the number of round trips can be determined from the total number of code symbols. The process and the device which are known from the abovementioned DE-OS 30 32 520 are not suitable for this, as the containers which are to be marked with a new code symbol are merely separated in each case, in order to be marked with a new code symbol elsewhere. Moreover, in the case of plastic bottles it would be desirable to increase the data content beyond the mere number of code symbols. In the case of bottles, this causes greater difficulties than with kegs, as the latter have a considerably larger diameter and therefore more space for the code than bottles.
A code symbol is known from DE-OS 39 14 440. This describes an optically machine-readable binary code and also a process for creating it and for determining its size and density. The code is formed from a chequerwork symbol which reproduces the data in the form of black and white squares. The binary code is dynamically variable is its size, its format and in the density of its data. The matrix has a periphery in which the data are contained. The periphery is provided with a density display for displaying the density of the data in the matrix. By using the density display and a dimension display, a scanning device can calculate the size and the data density of the binary code. This known binary code is not suitable for refillable containers such as, for example, plastic bottles, because it would not be possible to accommodate on the latter either a chequerwork matrix of black and white squares or an adequate number of such binary codes which are of an adequate size, so that the squares can also be sufficiently reliably detected.